Prior to the present invention, as shown by Abolins et al., U.S. Pat. No. 4,024,093, assigned to the same assignee as the present invention and incorporated herein by reference, flame retardant polyphenylene ether resin compositions were provided by employing a halogenated flame retardant, such as hexabromobiphenyl, and an effective amount of an organic iron compound, such as ferric stearate.
Japanese Pat. No. J59-226046 (June 7, 1983) shows that ammonium halides can be used as flame retardants for polyphenylene ether, styrene resin blends. For example, blends of 30 parts by weight of polyphenylene ether, 70 parts by weight of high impact polystyrene required 10 parts by weight of ammonium bromide or ammonium chloride for a satisfactory degree of flame retardancy.
It would be desirable to provide flame retardant blends of polyphenylene ether and styrene resin which were substantially free of significant amounts of polyhalogenated biphenyl or ammonium halides.
The present invention is based on our discovery that flame retardant blends of polyphenylene ether and styrene resin can be obtained exhibiting a V-0 rating in accordance with the UL-94 test as defined hereinafter, by incorporating into the polyphenylene ether/polystyrene resin blend, a minor amount of an iron halide, such as iron (III) bromide. We have found that as little as 0.1 to 3 parts of iron halide salt, per 100 parts by weight of polyphenylene ether-styrene resin blend will provide effective flame retardant results.
The expressions "V-0", "V-1", and "FOT" (average flame out time), as used hereinafter, describe flame retardance using 5"1/2".times.(1/8" or 1/16") test bars of blends of polyphenylene ether and polystyrene resin. The test bars are twice suspended over a 3/4" Bunsen burner flame in accordance with UL-94 Bulletin of Jan. 24, 1980 for Flammability of Plastic Materials. A UL-94 V-0 rating has the following criteria:
A. Not have any specimens which burn with flaming combustion for more than 10 seconds after either application of the test flame. PA0 B. Not have a total flaming combustion time exceeding 50 seconds for the 10 flame applications for each set of five specimens. PA0 C. Not have any specimens which burn with flaming or glowing combustion up to the holding clamp. PA0 D. Not have any specimens which drip flaming particles that ignite dry absorbent surgical cotton located 12 inches (305 mm) below the test specimen. PA0 E. Not have any specimens with glowing combustion which persists for more than 30 seconds after the second removal of the test flame.